Tungsten-halogen lamp with tantalum getter

ABSTRACT

A tungsten-halogen lamp having a tubular envelope filled with an inert gas and bromine and containing a getter in the form of a tantalum wire or foil fixedly supported in the lamp and so located that the operating temperature of the getter is between about 300*and 450*C.

United States Patent [191 Huston et al. I

TUNGSTEN-HALOGEN LAMP WITH TANTOLUM GETTER Inventors: Leroy S. Huston, Derry, N.H.;

Joseph S. Kulik, Jr., Amesbury, Mass.

GTE Sylvania Incorporated, Danvers, Mass.

Filed: July 13, 1973 Appl. No.: 378,974

Assignee:

US. Cl 313/179, 313/174, 313/222 Int. Cl. H01k 1/54, H01k 1/56 Field of Search 313/179, 178, 174, 222,

References Cited UNITED STATES PATENTS 2/l933 McGullough 313/178 X Primary Examiner.lames W. Lawrence Assistant Examiner--Wm. H. Punter Attorney, Agent, or Firm-Edward J. Coleman [5 7] ABSTRACT A tungsten-halogen lamp having a tubular envelope filled with an inert gas and bromine and containing a getter in the form of a tantalum wire or foil fixedly supported in the lamp and so located that the operating temperature of the getter is between about 300and 450C.

5 Claims, 4 Drawing Figures PATENTEL rm 1 9:914

PRIOR ART muumluuml IllllllllllllllllllH nlulllnmum FIG.2

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TUNGSTEN-HALOGEN LAMP WITH TANTOLUM GETTER BACKGROUND OF THE INVENTION This invention relates to incandescent lamps of the tungsten-halogen type and particularly to the gettering of such lamps.

In such lamps, the tungsten, which is normally evaporated from the filament during operation, combines with the halogen to form a gaseous halide and is thus kept from depositing on the wall of the lamp envelope. The halide normally has a regenerating action, being used over and over again, because when it returns to the hot filament or lead-in wires, the halide will decompose, depositing the tungsten on the filament or lead-in wires. This halogen cycle is well known, and lamps utilizing it have been on the market.

Such lamps have been made with various halogens, such as iodine and bromine. At the present state of the prior art, most halogen lamps using iodine have a longer life than those using bromine, especially when the halogen lamps are of the longer tubular type where the wall temperature is more uniform. Since bromine type lamps provide greater lumen output and are easier to manufacture, the natural trend is to convert from iodine type lamps to bromine. When long life is an important consideration, however, it has not hithertofore been practical to convert from iodine to bromine.

In the longer tubular lamps, the wall temperature is more uniform and does not permit the formation of stable oxides. As a .result, operation of the lamp leaves free oxygen which deteriorates the lamp filament and thereby significantly reduces the life of the lamp.

SUMMARY oF THE INVENTION Accordingly, it is an object of the present invention to provide an improved tungsten-halogen lamp with means for gettering impurities to extend the useful operating life thereof.

It is a particular object of the invention to provide a bromine type tungsten-halogen lamp containing means for gettering oxygen and hydrogen so as to considerably increase the life of the lamp.

A further object is to provide a reliable getter means for a tungsten-halogen lamp which is compatible with high speed lamp manufacturing operation.

These and other objects, advantages and features are attained, in accordance with the principles of the invention by inserting a piece of tantalum within the envelope of the tungsten-halogen lamp. In particular, effective gettering of oxygen and hydrogen in a bromine lamp is provided by locating the tantalum so that the operating temperature of the getter is between about 300 and 450C.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more fully described hereinafter in conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevational view of a representative tungsten-halogen lamp of the prior art;

FIG. 2 is an enlarged detail view of one end of the lamp of FIG. 1 modified to include a tantalum getter in accordance with the invention;

FIG. 3 is an enlarged detail view of the lamp end portion showing an alternative embodiment of the invention; and,

2 FIG. 4 is an enlarged detail view of the lamp end portion showing another alternative embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT Before discussing the manner in which a tantalum getter is used in accordance with the invention, the construction of a typical tungsten-halogen lamp of the prior art will now be discussed, with reference to FIG. 1. The lamp has an hermetically sealed, lighttransmitting envelope 2 of generally tubular shape with press seals 4 formed at each of its ends. A high melting point material, such as quartz, is generally used for the envelope, although with appropriate design, certain hard glasses, such as borosilicate or alumino silicate can also be used, as described in US. Pat. No. 3,641,386 and copending application Ser. No. 378,975, filed July I3, 1973 and assigned to the present assignee. The hermetically sealed envelope is filled with an inert gas, such as argon, nitrogen, krypton, or a mixture thereof, and a halogen additive such as iodine or bromine. The iodine fill is generally provided by inserting a predetermined amount of crystalline iodine in the lamp, and the bromine fill is typically provided in the form of a given mixture of hydrogen bromide. As described in the introductory paragraphs, the present invention is particularly useful as applied to a bromine lamp.

A coiled tungsten filament is longitudinally suspended within the envelope and is held in such position by a plurality of ring type tungsten wire spacers 8 disposed along the length of the tubular envelope and by a pair of electrically conducting tungsten inner leads 10 that are connected to the ends of the filament coil 6 and have their opposite ends embedded in the respec-v tive press seals 4. The embedded ends of the tungsten inner leads 10 are welded to strips of molybdenum foil 12 that are also embedded in the respective seals 4 and, in turn, are welded to our leads 14 of molybdenum. Interposed at each' weld between a lead and the foil 12 is a layer of platinum foil 16 serving as a flux for the weld. The platinum flux may also be used in the form of a paste.

According to the present invention, tantalum is controlably added to the lamp in various ways to act as a getter of oxygen and hydrogen. This gettering action is particularly useful in tubular bromine lamps for significantly increasing the operating life of these lamps. More specifically, it has been determined that tantalum will getter oxygen and hydrogen in appreciably amount if its temperature is above 300C. The optimum temperature is 350C but gettering action is satisfactory between 300 and 450C, while the getter action on bromine or nitrogen is negligible in this range. As the temperature rises above 450C, the gettering of bromine becomes appreciable. Consequently, in accordance with the invention, the location of the tantalum getter within the tungsten-halogen lamp envelope is controlled such that the operating temperature of the tantalum lies between 300 and 450C, and sufficient tantalum is employed to getter all the oxygen and hydrogen available, as empirically determined. The maximum amount of tantalum added is not critical in this controlled temperature approach.

Another possible approach is to control the amount of tantalum such that it will getter all available oxygen and hydrogen but be insufficient in quantity to getter a significant portion of the bromine. In this instance, the location of the tantalum is not critical, except that the operating temperature of the tantalum must be above 300C to effectively getter.

A preferred embodiment employing the controlled temperature approach is illustrated in FIG. 2, which shows an enlarged view of one end of the lamp of FIG. 1 modified according to the invention and representative of both ends of the lamp. At both ends of the lamp, a layer of tantalum foil 20 is interposed at the weld between the tungsten inner lead and the strip of molybdenum foil 12; that is, the tantalum is used as the intermediate weld layer in place of the platinum foil 16. At this location, the operating temperature of the tantalum should lie between about 300 and 450C.

The heat generated in making press seal 4 causes the embedded portion of the tungsten inner lead 10 to expand considerably during sealing. Consequently, if the envelope material is quartz, the much greater thermal expansion coefficient of tungsten will result in a void 22 in the press seal about lead 10 after the components contract upon cooling. As the operating temperature of the press seal region is much less than the temperature generated during press sealing, the void 22 about inner lead 10 between the tantalum foil 20 and the interior of the lamp continues to exist during lamp operation. It is this void 22 (shown greatly enlarged) which provides a passage between the tantalum foil 20 and the lamp interior for gettering oxygen and hydrogen within the envelope 2.

In a specific implementation of the embodiment of FIG. 2, a l/ 16 inch square of tantalum foil, 0.003 inch thick, is used as a getter 20 at each end of a 1,500 watt bromine lamp having a T3 size quartz envelope. The outside diameter of the envelope is about 0.375 inch; the overall length of the lamp is about 10 inches; and, a linear, single coil tungsten filament is employed, having a length of about 6 3 inches. Inner leads 10 are tungsten, and the filament is supported by thirteen ring type tungsten spacers 8. The foil strips 12 are molybdenum, as are the outer leads 14. The inert fill gas is argon, and the halogen is added in the form of hydrogen bromide. The total absolute fill pressure is about 2.5 atmospheres, with about 0.41 percent thereof being attributable to the halogen. During operation, the filament temperature was 2,900K, and the temperature of such tantalum getter 20 was about 350C. Upon life testing this gettered bromine lamp, it was found to have an extended life span similar to that of equivalent type iodine lamps. In addition, the bromine lamp continued to maintain its characteristic increased lumen output over equivalent type iodine lamps.

FIG. 3 shows an alternative embodiment, wherein the lamp of FIG. 1 has a piece of tantalum wire 24 anchored in the press seal 4 at each end of the lamp and located so that the operating temperature of the getter portion of the wire extending into the envelope interior is between about 300 and 450C. For convenience in assembly, the tantalum wire initially may be welded to the molybdenum foil 12, and thereafter both the foil 12 and tantalum wire 24 press sealed in the same operation. Both this approach and that of FIG. 2 assure consistent location of the tantalum wire in the desired temperature region of the lamp, and anchoring a portion of the tantalum in the press seal 4 effects a degree of temperature control by assuring a heat sinking capability to the temperature of the seal region.

FIG. 4 is another embodiment wherein a strip of tantalum foil 26 is welded to the molybdenum foil 12 and partially embedded in the press seal 4, with a portion extended well into the envelope cavity. In this case the temperature is not critical (except for being greater than 300C) but the total weight of tantalum in the lamp must be controlled (as empirically determined) so that there is a sufficient quantity to getter the available oxygen and hydrogen in the lamp, but an insufficient quantity to getter a significant portion of the bromine.

Although the invention has been described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention. For example, lamp configurations are contemplated wherein the getter of FIGS. 2-4 comprises a piece of tantalum located at just one end of the lamp.

What we claim is:

1. A tungsten-halogen incandescent lamp comprismg:

an hermetically sealed, light-transmitting envelope;

a fill of inert gas and halogen within said envelope,

said halogen being bromine;

a coiled tungsten filament supported within said envelope;

and a piece of tantalum supported within said envelope for gettering oxygen and hydrogen, said piece of tantalum being so located within said envelope that the operating temperature of the portion of said tantalum piece used for gettering is between about 300 and 450C.

2. A lamp according to claim 1 wherein at least one end of said envelope has a seal, and said piece of tantalum is a wire anchored in said seal and having a portion disposed as a getter within said envelope.

3. A lamp according to claim 1 wherein at least one end of said envelope has a seal, and said piece of tantalum is a strip of foil anchored in said seal and having a portion disposed as a getter within said envelope.

4. A lamp according to claim 1 further including an electrically conducting inner lead in said envelope, said lead being connected to one end of said tungsten filament and wherein at least one end of said lamp has a press seal, a molybdenum foil is embedded in said press seal, the other end of said inner lead enters said press seal and is welded to said molybdenum foil, said piece of tantalum is a layer of foil interposed at the weld between said molybdenum foil and said inner lead, and said press seal has a void about the portion of said inner lead entered therein whereby a passage is provided between said tantalum foil and the interior of said envelope for gettering oxygen and hydrogen in said envelope.

5. A lamp according to claim 1 wherein said envelope is substantially tubular, said inert gas is selected from the group consisting of argon, nitrogen, krypton and mixtures thereof, and said halogen is present in the form of hydrogen bromide.

. Attest:

U NITED STATES PATENT -oi nos} CERTIFICATE OF CORRECTION Patent No. K 5,849,687 Dated NOVEMBER 19, 1974 Inventor (s) LERQY S. HUSTON and JOSEPH S. KULIK, JR.

I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

54: In the Fifi tie:

Change TUNGSTEN-HALOGEN LAMP WITH "'I'ANTOLUM" GETTER To: TUNGSTEN-HALOGEN LAMP WITH -TANTALUM- GET'I'ER Signed sealed this 14th day of January 1975.

(SEAL) McCOY M. GIBSON-III. v c. MARSHALL mum Attosting Officer Comnisaioner of Patents USCOMM-DC 60376-P69 ul-sv GOVERNMENT PRINTING oFFlc: I!" o-scs-au FORM PO-IOSO (10-69) 

1. A TUNGSTEN-HALOGEN INCANDESCENT LAMP COMPRISING: AN HERMETICALLY SEALED, LIGHT-TRANSMITTING ENVELOPE; A FILL OF INERT GAS AND HALOGEN WITHIN SAID ENVELOPE, SAID HALOGEN BEING BROMINE; A COILED TUNGSTEN FILAMENT SUPPORTED WITHIN SAID ENVELOPE; AND A PIECE OF TANTALUM SUPPORTED WITHIN SAID ENVELOPE FOR GETTERING OXYGEN AND HYDROGEN, SAID PIECE OF TANTALUM BEING SO LOCATED WITHIN SAID ENVELOPE THAT THE OPERATING TEMPERATURE OF THE PORTION OF SAID TANTALUM PIECE USED FOR GETTERING IS BETWEEN ABOUT 300* AND 450*C.
 2. A lamp according to claim 1 wherein at least one end of said envelope has a seal, and said piece of tantalum is a wire anchored in said seal and having a portion disposed as a getter within said envelope.
 3. A lamp according to claim 1 wherein at least one end of said envelope has a seal, and said piece of tantalum is a strip of foil anchored in said seal and having a portion disposed as a getter within said envelope.
 4. A lamp according to claim 1 further including an electrically conducting inner lead in said envelope, said lead being connected to one end of said tungsten filament and wherein at least one end of said lamp has a press seal, a molybdenum foil is embedded in said press seal, the other end of said inner lead enters said press seal and is welded to said molybdenum foil, said piece of tantalum is a layer of foil interposed at the weld between said molybdenum foil and said inner lead, and said press seal has a void about the portion of said inner lead entered therein whereby a passage is provided between said tantalum foil and the interior of said envelope for gettering oxygen and hydrogen in said envelope.
 5. A lamp according to claim 1 wherein said envelope is substantially tubular, said inert gas is selected from the group consisting of argon, nitrogen, krypton and mixtures thereof, and said halogen is present in the form of hydrogen bromide. 